Development of a Pumpless Microfluidic System to Study the Interaction between Gut Microbes and Intestinal Epithelial Cells

Intestinal organ chips for disease modelling and personalized medicine

Alterations in intestinal structure, mechanics and physiology underlie acute and chronic intestinal conditions, many of which are influenced by dysregulation of microbiome, peristalsis, stroma or immune responses. Studying human intestinal physiology or pathophysiology is difficult in preclinical animal models because their microbiomes and immune systems differ from those of humans. Although advances in organoid culture partially overcome this challenge, intestinal organoids still lack crucial features that are necessary to study functions central to intestinal health and disease, such as digestion or fluid flow, as well as contributions from long-term effects of living microbiome, peristalsis and immune cells. Here, we review developments in organ-on-a-chip (organ chip) microfluidic culture models of the human intestine that are lined by epithelial cells and interfaced with other tissues (such as stroma or endothelium), which can experience both fluid flow and peristalsis-like motions. Organ chips offer powerful ways to model intestinal physiology and disease states for various human populations and individual patients, and can be used to gain new insight into underlying molecular and biophysical mechanisms of disease. They can also be used as preclinical tools to discover new drugs and then validate their therapeutic efficacy and safety in the same human-relevant model.

Recent Advances in Gut- and Gut-Organ-Axis-on-a-Chip Models

The human gut extracts nutrients from the diet while forming the largest barrier against the outer environment. In addition, the gut actively maintains homeostasis through intricate interactions with the gut microbes, the immune system, the enteric nervous system, and other organs. These interactions influence digestive health and, furthermore, play crucial roles in systemic health and disease. Given its primary role in absorbing and metabolizing orally administered drugs, there is significant interest in the development of preclinical in vitro model systems that can accurately emulate the intestine in vivo. A gut-on-a-chip system holds great potential as a testing and screening platform because of its ability to emulate the physiological aspects of in vivo tissues and expandability to incorporate and combine with other organs. This review aims to identify the key physiological features of the human gut that need to be incorporated to build more accurate preclinical models and highlights the recent progress in gut-on-a-chip systems and competing technologies toward building more physiologically relevant preclinical model systems. Furthermore, various efforts to construct multi-organ systems with the gut, called gut-organ-axis-on-a-chip models, are discussed. In vitro gut models with physiological relevance can provide valuable platforms for bridging the gap between preclinical and clinical studies.

Microfluidic gut-axis-on-a-chip models for pharmacokinetic-based disease models

The low success rate of new drugs transitioning from animal testing to human clinical trials necessitates the development of more accurate and representative in vitro models. Recent advances in multi-organ-on-a-chip technology offer promising avenues for studying complex organ-organ interactions. Gut-liver-on-a-chip systems hold particular promise for mimicking the intricate interplay between the gut and liver, which play crucial roles in nutrient absorption, drug metabolism, detoxification, and immune response. Here, we discuss the key components of the gut-liver axis, including the gut epithelium, liver cells, gut microbiota, and their roles in the organ functions. We then explore the potential of gut-liver-on-a-chip models to replicate the intricate interactions between the two organs for pharmacokinetic studies and their expansion to more complicated multi-organ models. Finally, we provide perspectives and future directions for developing more physiologically relevant gut-liver-axis models for more efficient drug development, studying liver diseases, and personalizing treatment strategies.

A generic pump-free organ-on-a-chip platform for assessment of intestinal drug absorption

Organ-on-a-chip technology has shown great potential in disease modeling and drug evaluation. However, traditional organ-on-a-chip devices are mostly pump-dependent with low throughput, which makes it difficult to leverage their advantages. In this study, we have developed a generic, pump-free organ-on-a-chip platform consisting of a 32-unit chip and an adjustable rocker, facilitating high-throughput dynamic cell culture with straightforward operation. By utilizing the rocker to induce periodic fluid forces, we can achieve fluidic conditions similar to those obtained with traditional pump-based systems. Through constructing a gut-on-a-chip model, we observed remarkable enhancements in the expression of barrier-associated proteins and the spatial distribution of differentiated intestinal cells compared to static culture. Furthermore, RNA sequencing analysis unveiled enriched pathways associated with cell proliferation, lipid transport, and drug metabolism, indicating the ability of the platform to mimic critical physiological processes. Additionally, we tested seven drugs that represent a range of high, medium, and low in vivo permeability using this model and found a strong correlation between their Papp values and human Fa, demonstrating the capability of this model for drug absorption evaluation. Our findings highlight the potential of this pump-free organ-on-a-chip platform as a valuable tool for advancing drug development and enabling personalized medicine.

Advanced Organotypic In Vitro Model Systems for Host-Microbial Coculture

In vitro model systems have been advanced to recapitulate important physiological features of the target organ in vivo more closely than the conventional cell line cultures on a petri dish. The advanced organotypic model systems can be used as a complementary or alternative tool for various testing and screening. Numerous data from germ-free animal studies and genome sequencings of clinical samples indicate that human microbiota is an essential part of the human body, but current in vitro model systems rarely include them, which can be one of the reasons for the discrepancy in the tissue phenotypes and outcome of therapeutic intervention between in vivo and in vitro tissues. A coculture model system with appropriate microbes and host cells may have great potential to bridge the gap between the in vitro model and the in vivo counterpart. However, successfully integrating two species in one system introduces new variables to consider and poses new challenges to overcome. This review aims to provide perspectives on the important factors that should be considered for developing organotypic bacterial coculture models. Recent advances in various organotypic bacterial coculture models are highlighted. Finally, challenges and opportunities in developing organotypic microbial coculture models are also discussed.

The Modular µSiM Reconfigured: Integration of Microfluidic Capabilities to Study In Vitro Barrier Tissue Models under Flow

Microfluidic tissue barrier models have emerged to address the lack of physiological fluid flow in conventional "open-well" Transwell-like devices. However, microfluidic techniques have not achieved widespread usage in bioscience laboratories because they are not fully compatible with traditional experimental protocols. To advance barrier tissue research, there is a need for a platform that combines the key advantages of both conventional open-well and microfluidic systems. Here, a plug-and-play flow module is developed to introduce on-demand microfluidic flow capabilities to an open-well device that features a nanoporous membrane and live-cell imaging capabilities. The magnetic latching assembly of this design enables bi-directional reconfiguration and allows users to conduct an experiment in an open-well format with established protocols and then add or remove microfluidic capabilities as desired. This work also provides an experimentally-validated flow model to select flow conditions based on the experimental needs. As a proof-of-concept, flow-induced alignment of endothelial cells and the expression of shear-sensitive gene targets are demonstrated, and the different phases of neutrophil transmigration across a chemically stimulated endothelial monolayer under flow conditions are visualized. With these experimental capabilities, it is anticipated that both engineering and bioscience laboratories will adopt this reconfigurable design due to the compatibility with standard open-well protocols.

Multi-Organ-on-a-Chip for Realization of Gut-Skin Axis

The concept of physiological link between the gut and the skin, known as the gut-skin axis, has been gaining more evidence recently. Although experimental data from animal and human studies support the existence of the gut-skin axis, in vitro model platforms that can test the hypothesis are lacking. Organ-on-a-chip offers the possibility of connecting different tissues and recapitulating interactions between them. In this study, we report a multi-organ chip that can capture the basic inter-organ communication between the gut and the skin. Its modular design enables separate culture and differentiation of the gut and skin tissues, and after assembly the two organs are connected via microfluidic channels than enables perfusion and mass transfer. We showed that the impairment of the gut barrier function exacerbated the adverse effect of fatty acids on skin cells, with decreased viability, increased level of cytokine secretion and human β-defensin-2 (hBD-2), an inflammatory dermal disease marker. Based on these results, we believe that our multi-organ chip can be a novel in vitro platform for recapitulating complex mechanisms underlying the gut-skin axis. This article is protected by copyright. All rights reserved.